Shock-wave and spalling phenomena in ultrafine-grained and coarse-grained (α + β) alloy Ti-Al-V treated by a nanosecond relativistic high-current electron beam

The results of experimental and theoretical research of shock-wave and spalling phenomena in ultrafine-grained and coarse-grained (α + β) alloy Ti–6.2% Al–4.0% V (wt %) treated by a nanosecond relativistic high-current electron beam are presented. Data on the dynamics of mass velocity, temperature and shock waves as well as on the interaction of the unloading wave with the rarefaction wave reflected from the back surface have been obtained for an axisymmetric position of the target. It is shown that the strain rate increase from 10−3 to 105 s−1 in the both grain structures does not change the fracture mechanism and the phase composition in the zone of spalling. The obtained theoretical dependence of the spalling layer thickness to the target thickness corresponds to experimental data

Investigation of structural-scale levels of spall fracture induced by a nanosecond relativistic high-current electron beam in ultrafine-grained Ti–Al–V–Mo alloy

The results of an experimental and theoretical study of shock-wave processes and spall fracture in an ultrafine-grained and coarse-grained (α + β) Ti–Al–V–Mo alloy under the action of a nanosecond relativistic high-current electron beam are reported. Mathematical modeling is performed to show that when an electron beam with a power density of 1.65 × 1010 W/cm2 impacts this alloy, a shock wave with a compression amplitude of 13 GPa appears and its reflection gives rise to a tensile wave. Its amplitude increases with decreasing target thickness. The calculated increase in the thickness of the spalled layer at the rear surface of the target corresponds to the experimental data. It is established experimentally that plastic deformation precedes the spall fracture sequentially at three structural-scale levels. At the beginning pores are formed and merge, then microcracks are formed at different angles to the back surface of the target between the pores, and then a macrocrack is formed. As a result, the macrocrack surface is not smooth but exhibits pits of ductile fracture

Characterization of hexamethyldisiloxane plasma polymerization in a DC glow discharge in an argon flow

This work aims to study hexamethyldisiloxane (HMDSO) plasma polymerization in a low-pressure glow discharge in a gas flow. HMDSO was activated in a plasma-chemical reactor with a DC glow discharge in an argon flow. The argon flow (the mass flow rate was 230 mg/min) was injected in the direction of the anode from the cathode. HMDSO vapors were injected into the plasma-chemical reactor either through the hollow cathode or through the inlet located between the cathode and the anode. Polymer coatings were deposited on the substrates located in a vacuum chamber. Plasma polymerization was characterized based on the mass of coatings deposited under varying external conditions: the HMDSO mass flow rate (1–10 mg/min), the average discharge current (6–60 mA), and the discharge power (6–30 W). The operation modes of the plasma-chemical system were determined. The chemical structure of the coatings was analyzed using the infrared spectroscopy. The processes occurring in different regions of the glow discharge and at the interface near the substrate surface are proposed. A DC glow discharge in a gas flow can be used for local deposition of polymer coatings on the surface of dielectric or conductive materials

Structure and chemical state of oxide films formed on crystalline TiNi alloy and glassy Ti-Ni-Ta-Si surface alloy

The stable oxide layers formed by chemical or electron-beam treatments of TiNi shape memory alloys are able to provide a good corrosion resistance and prevent release of toxic Ni. The mechanisms responsible for corrosion behavior of Ti-bearing alloys are currently not completely clear. In this work, the structure and electrochemical properties of surface oxides on TiNi alloy and Ti-Ni-Ta-Si surface alloy were examined. The glassy structure of the surface alloy was produced by a liquid phase mixing of Ti60Ta30Si10 (at.%) film with a TiNi substrate using a low-energy high-current electron beam. The reference electropolished TiNi alloy and the Ti-Ni-Ta-Si surface alloy exhibit thin (2-4 nm) glassy-crystalline oxide layers varying by chemistry and phase composition as confirmed using high-resolution transmission electron microscopy and x-ray photoelectron spectroscopy. It is shown that during anodic polarization in 0.9% NaCl and Lock-Ringer solutions, the oxide layer on the Ti-Ni-Ta-Si surface alloy possesses an enhanced passivation ability compared to the reference sample. We have revealed that the absence of oxidation species Ni2+ and the lower nickel concentration in the subsurface layer are closely related with corrosion resistance. A scheme describing the formation of corrosion products via transport of nickel ions through the free volumes (interstitial spaces, interfaces between clusters/particles) inside the oxide layer was proposed

The influence of electron-beam treatment on the structure of a TiNi powder alloy obtained by calcium-hydride reduction

The study of the influence of electron-beam treatment on the structural features of a TiNi powder alloy obtained by calcium-hydride reduction is carried out. It is found that electron-beam treatment leads to homogenization of the phase and chemical composition of the surface layer of the TiNi powder alloy, smoothing of the surface relief of TiNi powder particles, and the healing of the defects on their surface. It is shown by energy dispersive X-ray spectral microanalysis that the concentration of Ti in the surface layer increases. This is due to recrystallization of this layer containing Ti2Ni particles during its remelting under the influence of the high energy density of the electron beam during treatmen

Fracture of coarse-grained and ultrafine-grained titanium upon quasi-static and wave-impact loading

Results of experimental investigation of the regularities and mechanisms of fracture of coarse-grained and ultrafine-grained titanium upon wave-impact loading, exposure to a nanosecond relativistic high-current electron beam, and quasi-static tension are presented. Results of computer modeling of the shock wave generated upon exposure to the electron beam and of the spalling fracture of titanium targets with coarsegrained and ultrafine-grained structures are presented. The general regularities and special features of fracture are established for both grained structures under quasi-static and wave-impact loading